1. Field of the Invention
The present invention relates to a wireless communication terminal and a control method thereof, and particularly to location registration operation of a wireless communication terminal capable of reducing a load on a network.
2. Description of the Related Art
In a cellular phone system, a base station is located for each location area. A cellular phone present in the location area performs location registration with the base station at a fixed time interval. Moreover, when power of the cellular phone is switched on, the cellular phone first performs location registration with the base station. When the cellular phone moves to another location area, the cellular phone performs location registration with a base station in the location area. When the location area includes a no service area and a service area, such location registration as described above is performed as soon as the cellular phone moves from the no service area to the service area.
Japanese Patent Laid-Open No. 2002-165260 discloses an example of location registration method of a cellular phone. In this example, when a network is in a congestion state, location registration is temporarily suspended based on information from the network. When detecting that the congestion state has been avoided, the cellular phone performs location registration. This method can reduce a load on the network situated in the congestion state.
However, even in the case where the network is not in the congestion state, when a plurality of the cellular phones perform location registration simultaneously, the load on the network is increased instantly, and there is a possibility that the congestion state may occur. FIG. 1 shows an example of such a problem. This example shows location registration operations of three cellular phones. A cellular phone MS3 is turned on at a time Ta. Thereafter, cellular phones MS1 and MS2 are turned on simultaneously at a time Tb. The cellular phone MS3 starts location, registration at the turn-on time Ta. The cellular phones MS1 and MS2 start location registration simultaneously at the turn-on time Tb. Based on these location registration operations, respective IDs of the cellular phones MS1, MS2 and MS3 and an ID of a location area B are registered in an administrative server through a network. While the cellular phones MS1, MS2 and MS3 keep on staying in the location area B, location registration is performed periodically at every time an interval T1 has elapsed; the first of which starts from the first registration times of the respective cellular phones. When the cellular phones move to a location area A, the cellular phones MS1, MS2 and MS3 perform location registration simultaneously at a time Tf. Furthermore, subsequent periodic location registration operations are also performed simultaneously. As described above, when the plurality of cellular phones change the location area simultaneously, the location registration operations immediately after the change occur simultaneously, and the subsequent periodic location registration operations also occur simultaneously. Therefore, the load on the network increases.
For example, in the case where there is a railway tunnel on a boundary between location areas, at an instant when a train comes out of the tunnel, cellular phones on the train perform location registration simultaneously in accordance with a change of the location area. At this time, a large load occurs instantly on the network. Moreover, when an audience having cellular phones comes out of a no service area such as a theater and a cinema, there is a possibility that location registration operations of a large number of cellular phones may occur nearly simultaneously. In this case also, the load on the network is increased temporarily, and there is a possibility that stable communications may come to be impossible.